Heretofore, phosphate-based acrylic adhesive promoters have been utilized to vastly improve the adhesion of methacrylate structural adhesives to metals including metals coated with mill oils from stamping and cutting operations. Phosphonic acid based adhesion promoters have not been as readily available. There is a desire for improved corrosion resistance in adhesively bonded metal assemblies. The phosphate ester linkage is suspected as being a weak link in the adhesives using phosphate-based adhesion promoters.
U.S. Pat. No. 4,223,115 relates to structural adhesive systems for metal-bonding applications comprising a solution or dispersion of a polymeric material in a monomer copolymerizable therewith having incorporated therein certain phosphorus-containing compounds that are characterized by an unexpected ability of providing strong adhesion to untreated metal surfaces without adversely affecting adhesive performance, including resistance to deleterious environments. The environmental resistance of the described adhesives can be further improved by the addition of one or more polybasic lead salts, metal molybdates and metal phosphates.
U.S. Pat. No. 6,326,453 relates to a novalak-type phenol resin reportedly with less unreacted phenol and a narrow molecular weight distribution that is reportedly produced in high yield by reaction of a phenol with an aldehyde using an organophosphoric acid as a catalyst, while keeping a water concentration of reaction system at not more than 30% by weight and a reaction temperature at 110° C. to 200° C.
U.S. Pat. No. 7,910,024 relates to compositions and methods for inhibiting corrosion of corrodible metals present in contact with water in cooling water and other water storage systems. The compositions include concentrated stannous salts and agents to solubilize such salts.